Stabilization of lubricants



ilnited; rates Pa ent 3,@78,Z3@ Patented Feb. 19, 1953 Delaware N Drawing. Filed July 13, 1959, Ser. No. 3 26,4ii8

14 Claims. (Ci. 252-421) This invention relates to the stabilization of lubricants and more particularly to a synergistic inhibitor composition and the use thereof in lubricants.

In recent years, stringent requirements for lubricants in certain applications have resulted in the availability of a new class of lubricants referred to in the art as synthetic lubricants. These lubricants do not necessarily replace petroleum oils in conventional usage, but are designed for special applications where the petroleum oils do not function to a satisfactory degree. These synthetic lubricants have found particular use in winter-grade crankcase oils, turbo-engine oils, aviation instruments, automatic weapons, etc. For example, aircraft gas turbines require oils capable of providing satisfactory lubri cation at temperatures ranging as low as 65 F. and as high at 275 F. during use. Temperatures up to 500 F. are encountered for intervals of from one to two hours during shut-down. Petroleum lubricants are unsatisfactory at high altitudes or in the winter season for use in machine guns and automatic cannons which frequently could not be made to fire because of congealed lubricants. Because they are used under such stringent conditions, the synthetic lubricants may undergo undesirable deterioration including, for example, formation of deposits, discoloration, change of viscosity, etc. While the features of the present invention are particularly applicable to the stabilization of synthetic lubricants, it is understood that they also may be used for the stabilization of petroleum lubricants.

The synthetic lubricants are of varied types including aliphatic esters, polyalkylene oxides, silicones, esters of phosphoric and silicic acids, highly fluorine-substituted hydrocarbons, etc. Of the aliphatic esters, di-(Z-ethylhexyl) sebacate is being used on a comparatively large commercial scale. Other aliphatic esters include dialkyl azelates, dialkyl suberates, diaikyl pimelates, dialkyl adipates, dialkyl glutarates, etc. Specific examples of these esters include dihexyl azelaote, di-(Z-ethylhexyl) azelate, di-3,5,5-trimethylhexyl glutarate, di-3,5,5-trirnethylpentyl glutarate, di-(Z-ethylhexyl) pimelate, di-(Z-ethylhexyl) adipate, triamyl tricarballylate, pentaerythritol tetracaproate, dipropylene glycol dipelargonate, l,5-pentanediol-di-(Z-ethylhexanonate), etc. The polyalkylene oxides include polyisopropylene oxide, polyisopropylene oxide diether, polyisopropylene oxide diester, etc. The silicones include methyl silicone, methylphenyl silicone, etc., and the silicates include for example, tetraisooctyl silicate, etc. The highly fiuorinated hydrocarbons include fluorinated oil, perfiuorohydrocarbons, etc. An syn thetic lubricant proposed for use in high temperature service as, for example, jet fuel lubrication, etc., is pentaerythritol esters.

The present invention also is applicable to the stabilization of greases made by compositing metallic soaps with the synthetic lubricating oils described above and are referred to herein as synthetic greases. These metal base synthetic greases may be further classified as lithium base synthetic grease, sodium base synthetic grease, calcium base synthetic grease, barium base synthetic grease, strontium base synthetic grease, aluminum base synthetic grease, etc. These greases are solid or semi-solid gels and, in general, are prepared by the addition to the synthetic lubricating oil of hydrocarbon-soluble metal soaps or salts of higher fatty acids as, for example, lithium stearate, calcium stearate, aluminum naphthenate, etc. The grease also may contain thickening agents such as silica, carbon black, polyacrylates, talc, etc. Again, while the present invention is particularly applicable to the stabilization of synthetic greases, they also may be used in petroleum base grease.

It is general practice to incorporate an antioxidant in synthetic lubricants in order to improve the stability thereof. Research continues to search for even better inhibitors in order to further improve the synthetic lubricants and permit their use for longer periods of time in present applications, as well as to permit their use under even more severe conditions as, for example, in the engines of the future which are being developed to operate at peak eificiency at high altitudes. It is important that the synthetic lubricant under these conditions is stable, retains its lubricity properties, does not develop deposit formation, retains its desirable viscosity, etc.

It now has been found that a synergistic composition of both antioxidant and certain nitrogen-containing polymers impart to the synthetic lubricant a considerably improved stability, much greater than obtained through the use of the antioxidant alone. In face, this synergistic effect is surprising because the polymers themselves do not improve the stability of the synthetic lubricant to any substantial extent. Normally it would be predicted that this mixture would not be any better than the antioxidant alone. Accordingly, it is surprising that these great improvements in the stability of the lubricant are obtained through the use of the novel inhibitor mixture of the present invention.

In one embodiment the present invention relates to a method of stabilizing a lubricant which comprises incorporating therein a stabilizing concentration, in a synergistic proportion, of an antioxidant and a synergist comprising a polymer containing a basic nitrogen.

In a specific embodiment the present invention relates to a method of stabilizing di-(Z-ethylhexyl) sebacate which comprises incorporating therein a stabilizing concentration, in a synergistic proportion, of phenothiazine and a polymeric condensation product of epichlorohydrin and N-tallow amine.

In another specific embodiment the present invention relates to a method of stabilizing lithium base grease which comprises incorporating therein a stabilizing concentration, in a synergistic proportion, of phenothiazine and a polymeric condensation product of lauryl methacrylate and beta-diethylaminoethyl methacrylate.

In another embodiment the present invention relates to a lubricant containing a stabilizing concentration of the synergistic inhibitor composition herein defined.

Any suitable antioxidant may be used in the novel stabilizing composition of the present invention. Preferred antioxidants for synthetic lubricants include 1) phenothiazine, (2) diaminodiphenylmethanes, (3) diarninodiphenyl ethers, (4) diaminodiphenyl sulfides, and (5) dipyridylamine. Phenothiazine is presently being used as an antioxidant in synthetic lubricants and, accordingly, is particularly preferred for use in the present invention. As will be shown in the appended examples, the potency of phenothiazine to impart stability properties to the synthetic lubricant is considerably enhanced when used in admixture with the synergist and, as hereinbefore set forth, this is surprising because the polymeric condensation product is substantially of no value for this purpose when used by itself.

Any suitable diaminodiphenylmethane may be used as the antioxidant component of the novel inhibitor composition of the present invention. Particularly preferred diaminodiphenylmethanes include N,N' di isopropyldiaminodiphenyl methane, N,N'-di-sec-butyl diaminodiphenylmethane, N,N'-di sec-amyl diaminodiphenylmethane, N,N'-di-sec-hexyl-diaminodiphenylmethane, N,N'-disec-heptyl-diaminodiphenylmethane, N,N-di-sec-octy1-diaminodiphenylmethane, N,N dl sec-nonyl-diaminodiphenylmethane, N,N-di sec-decyl-diaminodiphenylmethane, N,N-di-sec-undecyl-diarninodiphenylmethane, N,N'- di-sec-dodecyl diaminodiphenylmethane, N,N'-di-sec-tridecyl-diaminodiphenylmethane, N,N'-di-sec-tetradecyl-di aminodiphenylmethane, etc. Other antioxidants include N,N-di-cyclohexyl diaminodiphenylrnethane and alkyl ated derivatives thereof. The amino groups are preferably in the 4,4'- and/ or 2,4-positions. It is understood that other suitable diaminodiphenylmethanes may be used in some applications. Even though the diaminodiphenylmethane may be of lower original potency, the use thereof in combination with the synergist may produce a final composition of sufficient potency to satisfy the requirements of many uses.

Any suitable diaminodiphenyl ether may be used as the antioxidant component of the inhibitor composition. Preferred diaminodiphenyl ethers include N,N-di-isopropyl-diaminodiphenyl ether, N,N-di-sec-butyl-diaminodiphenyl ether, N,N'-di-sec-amyl-diaminodiphenyl ether, N, N-di-sec-hexyl-diarninodiphenyl ether, N,N-di-sec-heptyldiaminodiphenyl ether, N,N-di-sec-octyl-diaminodiphenyl ether, N,N'-di-sec-nonyl-diaminodiphenyl ether, N,N'-disec-decyl-diaminodiphenyl ether, N,N'-di-sec-undecyldiaminodiphenyl ether, N,N'-di-sec-dodecyl-diaminodiphenyl ether, N,N-di-sec-tridecyl-diaminodiphenyl ether, N,N'- di-sec-tetradecyl-diaminodiphenyl ether, etc. Other antioxidants include N,N'-di-cyclohexyl diaminodiphenyl ether and alkylated derivatives thereof. The amino groups are preferably in the 4,4'- and/or 2,4'-positions. Here again, in some cases diaminodiphenyl ethers of lower original potency may be used because of the improved properties imparted through the use of the synergist.

. Any suitable diaminodiphenyl sulfide may be used as the antioxidant component of the inhibitor composition. Preferred diaminodiphenyl sulfides include N,N-'di-isopropyl-diaminodiphenyl sulfide, N,N' di sec-butyl-diaminodiphenyl sulfide, N,N-di-sec-amyl-diamiuodiphenyl sulfide, N,N'-di-sec-hexyl-diaminodiphenyl sulfide, N,N' di-sec-heptyl-diaminodiphenyl sulfide, N,N'-di-sec-octyl-diaminodiphenyl sulfide, N,N'-di-sec-nonyl-diaminodiphenyl sulfide, N,N'-di-sec-decyl-diaminodiphenyl sulfide, N, N-di-sec-undecyl-diaminodiphenyl sulfide, N,N'-di-secdodecyl-diarninodiphenyl sulfide, N,N'-di-sec-tridecyl-diaminodiphenyl sulfide, N,N-di-sec-tetradecyl-diaminodiphenyl sulfide, etc. Other antioxidants include N,N-dicyclohexyl diaminodiphenyl sulfide and alkylated derivatives thereof. Here again, in some cases, diaminodiphenyl sulfides of lower potency may be used because of the increased properties imparted thereto by the synergist.

The above antioxidants are preferred for use in the inhibitor composition of the present invention. However, it is understood that any other suitable antioxidant may be employed. Also, it is understood that the different antioxidants are not necessarily equivalent, either as for use as antioxidants or in regard to their susceptibility to the synergist. However, the synergistic mixture will result in an inhibitor composition of greater potency than obtained through the use of antioxidant alone.

Any suitable polymer containing a basic nitrogen may be utilized as the synergistic component of the inhibitor composition. Reference to basic nitrogen is used in a generic sense to include the primary, secondary and tertiary amines. Preferred polymeric condensation products comprise those produced by (1) polymeric condensation of an unsaturated compound having a polymerizable ethylenic linkage and an unsaturated compound having a polymerizable ethylenic linkage and a basic nitrogen, (2) the polymeric condensation of an epihalohydrin and an amine, and (3). the polymeric condensation of a vinylalkyl ether or other compound having a polymerizable ethylenic linkage and a dicarboxylic acid anhydride with an amine.

Any suitable polymeric condensation product formed by the reaction of (a) an unsaturated compound having a polymerizable ethylenic linkage and (b) an unsaturated compound having a polymerizable ethylenic linkage and a basic nitrogen may be used. Examples of the first mentioned unsaturated compound include saturated and unsaturated long chain esters of unsaturated carboxylic acids such as Z-ethylhexyl acrylate, nonyl acrylate, decyl acrylate, undecyl acrylate, dodecyl acrylate, tridecyl acrylate, tetradecyl acrylate, pentadecyl acrylate, hexadecyl acrylate, heptadecyl acrylate, octadecyl acrylate, etc., and particularly methacrylates including n-octyl methacrylate, n-nonyl methacrylate, 3,5,5-trimethyll1exyl methacrylate, n-decyl methacrylate, sec-capryl methacrylate, lauryl methacrylate, dodecyl methacrylate, tridecyl methacrylate, tetradecyl methacrylate, pentadecyl methacrylate, hexadecyl methacrylate, cetyl methacrylate, heptadecyl methacrylate, octadecyl methacrylate, 9-octa decenyl methacrylate, etc.; unsaturated esters of longchain carboxylic acids such as vinyl laurate, vinyl stearate; long-chain esters of vinylene dicarboxylic acids such as methyl lauryl fumarate; N-long-chain hydrocarbon substituted amides of unsaturated acids such as N-octadecyl acrylamide; long-chain monoolefins such as the alkyl or acyl substituted styrenes as, for example, dodecyl styrene, and the like. A particularly preferred compound is laury methacrylate and more particularly technical lauryl methacrylate which is obtained by esterification of a commercial mixture of long-chain alcosols in the C to C range derived from coconut oil. The technical lauryl methacrylate is available commercially at a lower price and, accordingly, is preferred. A typical technical lauryl methacrylate will contain in the ester portion carbon chain lengths of approximately 3% C10, 61% C12, 23% C14, C16, and 2% C18.

Examples of the second mentioned unsaturated compounds (those containing a basic nitrogen) include p-(beta-diethylaminoethyl)-styrene; basic nitrogen-containing heterocycles carrying a polymerizable ethylenically unsaturated substituent such as the vinyl pyridines and the vinyl alkyl pyridines as, for example, 2-vinyl- S-ethyl pyridine; esters of basic amino alcohols with unsaturated carboxylic acids such as the alkyl and cycloalkyl substituted aminoalkyl and amino cycloalkyl esters of the acrylic and alkacrylic acids as, for example, betamethaminoethyl acrylate, beta-diethylaminoethyl methacrylate, 4-diethylaminocyclohexyl methacrylate, betabeta-didodecylaminoethyl acrylate, etc.; unsaturated ethers of basic amino alcohols such as the vinyl ethers of such alcohols as, for example, beta-aminoethyl vinyl ether, beta-diethylaminoethyl vinyl ether, etc.; amides of unsaturated carboxylic acids wherein a basic amino substituen-t is carried on the amide nitrogen such as N-(betadimethylaminoethyl)-acrylamide; polymerizable unsaturated basic amines such as diallylamine, and the like.

The above polymeric condensation product is prepared in any suitable manner and generally by heating the reactants at a temperature of from about to about F. for a period of time ranging from two to fortyeight hours or more, preferably in the presence of a catalyst or initiator such as benzoyl peroxide, tertiary butyl peroxide, azo compounds as alpha,alpha'-azo-diisobutyronitrile, etc. When desired, the polymerization may be effected in the presence of a solvent and particularly aromatic hydrocarbons, including, for example, benzene, toluene, xylene, cumene, decalin, naphtha, etc.

Any suitable polymeric condensation product of an epihalohydrin compound and an amine may be used in the inhibitor composition of the present invention. A preferred epihalohydrin compound is epichlorohydrin. Other epichlorohydrin compounds include 1,2-epi-4- chlorobutane, 2,3-epi-4-chlorobutane, 1,2-epi-5-chloropentane, 2,3-epi-5-chloropentane, etc. While the chloro derivatives are preferred, it is understood that the corresponding bromo and iodo compounds may he employed in some cases.

One mole proportion of the epihalohydrin compound is reacted with one mol proportion of a suitable amine. Preferred amines include primary alkyl amines and preferably those containing from about twelve to about forty carbon atoms per molecule. Illustrative primary alkyl amines include dodecyl amine, tridecyl amine, tetradecyl amine, pentadecyl amine, hexadecyl amine, heptadecyl amine, octadecyl amine, nonadecyl amine, eicosyl amine, heneicosyl amine, docosyl amine, tricosyl amine, tetracosyl amine, pentacosyl amine, hexacosyl amine, heptacosyl amine, octacosyl amine, nonacosyl amine, triacontyl amine, hentriacontyl amine, dotriacontyl amine, tritriacontyl amine, tetratriacontyl amine, pentatriacontyl amine, hexatriacontyl amine, heptatriacontyl amine, octatriacontyl amine, nonatriacontyl amine, tetracontyl amine etc. Conveniently the long chain amines are prepared from fatty acids or more particularly from mixtures of fatty acids formed as products or by-products. Such mixtures are available commercially, generally at lower prices and, as another advantage of the present invention, the mixtures may be used without the necessity of separating individual amines in pure state.

An example of such a mixture is hydrogenated tallow amine which is available under various trade names including Alamine l-l26D and Armeen ETD. These products comprise mixtures predominating in alkyl amines containing sixteen to eighteen carbon atoms per alkyl group, although they contain a small amount of alkyl groups having fourteen carbon atoms.

Illustrative examples of secondary amines, which may be reacted with the epihalohydrin compound, include di- (dodecyl) amine, di-(tridecyl) amine, di-(tetradecyl) amine, cli-(pentadecyl) amine, di-(hexadecyl) amine, di- (heptadecyl) amine, di-(octadecyl) amine, di-(nonadecyl) amine, di-(eicosyl) amine, etc. In another embodiment, which is not necessarily equivalent, the secondary amine will contain one alkyl group having at least twelve carbon atoms and another alkyl group having less than twelve carbon atoms. Illustrative examples of such compounds include propyl dodecyl amine, butyl dodecyl amine, arnyl dodecyl amine, butyl tridecyl amine, amyl tridecyl amine, etc. Here again, mixtures of secondary amines are avail able commercially, usually at a lower price, and such mixtures may be used in accordance with the present invention. An example of such a mixture available commercially is Armeen ZHT which consists primarily of dioctadecyl amine and dihexadecyl amine.

Preferred examples of N-alkyl polyamines, which may be reacted with the epihalohydrin compound, comprise N-alkyl-1,3-diaminopropanes in which the alkyl group contains at least twelve carbon atoms. Illustrative examples include N-dodecyl-1,3-diaminopropane, N-tridecyl-1,3-diaminopropane, N-tetradecyl-l,3 -diaminopropane, N-pentadecyl-l,3-diaminopropane, N-hexadecyl-l ,3 -diaminopropane, N-heptadecyl- 1 ,3-diaminopropane, N-octadecyl-l,3-diaminopropane, N-nonadecyl-l ,S-diamiuopropane, N -eicosyl-1,3-diaminopropane, N-heneicosyl-1,3-diaminopropaue, N-docosyll ,3-diaminopropane, N-tricosyl-l,3-diaminopropane,

- N-tetracosyl-l,3-diaminopropane,

N-pentacosyl-l,3-diaminopropane, etc.

As before, mixtures are available commercially, usually at lower prices, of suitable compounds in this class and advantageously are used for the purposes of the present invention. One such mixture is Duomecn T which is N-tallow-1,3-diami11opropane and predominates in alkyl groups containing sixteen to eighteen carbon atoms each,

- 350 F. with stirring.

although the mixture contains a small amount of alkyl groups containing fourteen carbon atoms each. Another mixture available commercially is N-coc0-1,3-diaminopropane which contains alkyl groups predominating in twelve to fourteen carbon atoms each. Still another example is N-soya-l,S-diaminopropane which predominates in alkyl groups containing eighteen carbon atoms per group, although it contains a small amount of alkyl groups having sixteen carbon atoms. It is understood that corresponding N-alkyl diaminobutanes, N-alkyl diaminopentanes, N-alkyl diaminohexanes, etc. may be employed. In still another embodiment two diiferent amines may be reacted with the epihalohydrin compound, the second amine being selected from those hereinbefore set forth or comprising alkylene polyamines including ethylene diamine, diethylene triamine, triethylene tetramine, tetraethylene pentamine, etc., similar propylene and polypropylene polyamines, butylene and polybutylene polyamines, etc.

The epihalohydrin and amine are reacted in any suitable manner. In a preferred embodiment, the reactants are prepared as solutions in suitable solvents, particularly alcohols such as ethanol, propanol, butanol, etc., and one of the solutions is added gradually, with stirring, to the other solution, and reacted at a temperature of from about 60 to about 210 F. and preferably to about 210 F., and for a sufiicient time to effect polymer formation, which generally will range from about two andpreferably from about four to twenty-four hours or more.

Any suitable polymeric condensation product of a vinylalkyl ether or other compound having a polymerizable ethylenic linkage including, for example, diisobutylone, various methacrylates and acrylates, etc. and a dicarboxylic acid anhydride with an amine may be utilized as the syner istic component of the inhibitor composition of the present invention. Maleic anhydride is particularly preferred as the dicarboxylic acid anhydride. Other anhydrides include citraconic anhydride, etc. Any suitable vinylalhyl other may be used. Vinylrnethyl ether is particularly preferred. Other others include vinylethyl ether, vinylpropyl ether, vinylbutyl ether, etc., allylmethyl ether, allylethyl ether, allylpropyl ether, allylbutyl ether, etc., propenylmethyl ether, pro-penylethyl ether, propenylpropyl ether, propenylbutyl ether, etc. While the polymeric reaction product of the anhydride and other then is condensed with an amine, in some cases it is desirable to first react the polymer with an alcohol and then react the resultant product with the amine. Any suitable alcohol may be used and prefeably comprises alkyl alcohol having from about six to about twenty carbon atoms, thus including hexanol, heptanol, octanol, nonanol, decanol, undecanoi, dodecanol, tridecanol, tetradecanol, pentadecanol,

hexadecanol, heptadecanol, octadecanol, nonadeconal, eicosanol, etc. The polymer of anhdyride and ether, or the polymer further reacted with an alcohol, is then reacted with a suitable amine. The amine preferably is selected from those hereinbeio-re set forth in connection with the description of the condensation of epihalohydrin and amine.

The polymerization of anhydride and other may be effected in any suitable manner and generally in substantially the some manner as heretofore described in connection with the copolymer of lauryl methacrylate and beta-diethylaminoethyl methacrylate. When employed, reaction of the polymer with an alcohol is effected in any suitable manner'and generally by reacting the alcohol and polymer at a temperature of from about 250 to about The temperature must be sufiicient to etlect the desired esterification. Preferably at least one mol proportion of alcohol is utilized per mol proportion of each recurring unit in the polymer, although a lower proportion may be used, if desired.

The reaction of the polymer or of the polymer-alcohol condensation product with the amine is effected in any suitable manner and preferably in the presence of an aromatic solvent. Depending upon the particular solvent employed, the reaction temperature will range from about 175 to about 400 F. Xylene is a particularly preferred solvent and, when used, the reaction is effected at a temperature of from about 280 to about 320 F.

The specific polymeric condensation products hereinbefore set forth are preferred. It is understood that other suitable condensation products containing basic nitrogen may be utilized. For example, maleic anhydride may be copolymerized with an olefin including ethylene, propylene, butylene, etc. or a diolefin including butadiene, isoprene, etc., and either first condensed with an alcohol and then reacted with the amine or reacted directly with the amine. It is understood that the difierent polymeric condensation products are not necessarily equivalent in their synergistic effects with the antioxidants in the same or different substrates.

The proportions of antioxidant and synergist may vary over a wide range and thus may range from 0.1 to 4 and preferably from 0.5 to 2 parts by weight of synergist per one part by weight of antioxidant, although in some cases lower or higher proportions may be used. These proportions are based upon the active ingredient exclusive of solvent. While the antioxidant and synergist may be added separately to the lubricant, it generally is preferred to form a suitable mixture of the antioxidant and synergist and add the mixture to the lubricant. When desired, the antioxidant and synergist may be prepared as a solution in a suitable solvent, particularly aromatic hydrocarbons and more particularly an aromatic hydrocarbon as hereinbefore set forth, and marketed or used as a single product. Conveniently, the same solvent is used in the final solution as used in the preparation of one or both of the antioxidant and synergist. The solution may comprise from about 10% to about 90% and preferably from about 25% to about 75% by weight of active ingredient.

The inhibitor composition will be used in the substrate in an amount sufiicient to obtain the desired stabilization. This stabilizing concentration will be within the range of from about 0.001% to about 5% and preferably from about 0.1% to about 3% by weight of the lubricant. The inhibitor composition is added to the lubricant in any suitable manner and preferably with intimate mix- 'ing in order to obtain distribution of the inhibitor composition in the lubricant. In some cases the inhibitor composition may be added to the lubricant during the manufacture thereof. For example, when used in grease, the inhibitor composition may be added to one or more of the components before final compositing thereof.

It is understood that the inhibitor composition of the present invention may be used along with other additives incorporated in the lubricant. For example, a metal deactivator, dye, viscosity index improver, pour point depressant, antifoaming additive, lubricity and extreme pressure additive, antiscutfing additive, etc. may be incorporated in the synthetic lubricant. When desired, the inhibitor composition of the present invention may be prepared as a mixture with one or more of these other additives and incorporated in this manner in the lubricant.

The following examples are introduced to illustrate further the novelty and utility of the present invention but not with the intention of unduly limiting the same.

EXAMPLE I The antioxidant component of the inhibitor composition of this example was phenothiazine. The synergistic component of the inhibitor composition was the condensation product of epichlorohydrin and hydrogenated tallow amine. The hydrogenated tallow amine is marketed commercially as Armeen HTD and, as hereinbefore set forth, is a mixture of primary amines predominating in sixteen to eighteen carbon atoms per alkyl group. The condensation was effected by first forming a solution of two mols of epichlorohydrin in 600 cc. of a solvent mix- '--of synthetic lubricating oil.

S ture comprising 400 cc. of xylene and 200 cc. of 2-propanel. A separate solution of two mols of Armeen HTD was prepared in an equal volume of xylene. One mol of 'the latter solution was added gradually to the epichlorohydrin solution, with stirring and heating at l40 F. for a period of 2.5 hours. Then another mol of Armeen HTD was added gradually to the reaction mixture, stirred and reacted at F. for 2.5 hours. One mol of sodium hydroxide then was added with stirring and heating at l95 F. for 3.5 hours, after which another mol of sodium hydroxide was added and the mixture stirred and reacted at 185-195" F. for one hour. Following completion of the reaction, the mixture was cooled, filtered, and the filtrate then was distilled under vacuum to remove the alcohol and xylene.

The resultant product was a hard, waxy, brittle solid of light amber color containing 3.11 meq./g. of basic nitrogen.

Phenothiazine, the copolymer of epichlorohydrin and tallow amine prepared in the above manner, and a mixture containing approximately 1% by weight of each were separately evaluated in synthetic lubricating oil.

'The synthetic lubricating oil was dioctyl sebacate marketed under the trade name of Plexol 201. The evaluation was made in accordance with an xygen Stability Test, in which a 100 cc. sample of the synthetic lubricating oil is placed in a bath maintained at 400 F. and air is blown therethrough at a rate of 5 liters of air per hour. The sample of synthetic lubricating oil is examined periodically and the time to reach an acid number of 5 is reported. It is apparent that the longer the time required to reach an acid number of 5 the more stable is the sample In other words, it takes longer for the more stable oil to deteriorate.

In addition to determining the acid number, the percent viscosity change and the pentane insolubles were also determined. The results of these evaluations, along with an evaluation of the sample of lubricating oil without additive, are reported in the following table:

Table l Sample Hours to Percent Percent No. Additive acid viseoiity pcntane number change insolubles 1 None 9 1% by weight of pheno- 75 16.8 after 0.9 after thiazine 75 hours. 75 hours.

3. 1% by weight of the poly- 11 merie condensation product prepared in the above manner.

4 1% by weight of pheno- 111 3.2 after 0.8 after thiazine plus 1% by 96 hours. 96 hours. weight of the polymeric condensation product prepared in the above manner.

1 The phenothiazine in all cases was used in a concentration of 0.0033 mols per 100 cc. of the lubricating oil. This is approximately 1% by weight; thereof.

From the data in the above table, it will be noted that the polymeric condensation product alone was of substantially no value in increasing the time to reach an acid number of 5. Surprisingly, in admixture with phenothiazine, the polymeric condensation product served to extend the time to reach an acid number of 5 from 75 to 111 hours. It will be noted that this is a considerable increase and imparts much higher stability to the lubricating oil.

From the data in the above table, it also will be noted that the viscosity change after treatment at 400 F. was 16.8% for the lubricating oil containing phenothiazine alone (sample No. 2) and only 3.2% for the lubricating oil containing the synergistic mixture (sample No. 4). Also, it is to be noted that sample No. 4 was determined after 96 hours, whereas sample No. 2 was determined after 75 hours. As hereinbefore set forth, it is important that the lubricating oil does not change in viscosity because it either becomes too fluid and loses its lubricity properties, or becomes too heavy and will not flow readily or clogs the equipment parts, such as filters, etc. Also, the synergistic composition served to produce a lower percent of pentane insoluble material after 96 hours (sample No. 4) than obtained with phenothiazine alone after 75 hours (sample No. 2).

EXAMPLE H The inhibitor composition of this example was phenothiazine as the antioxidant component and a copolymer of lauryl methacrylate and particularly diethylaminoethyl methacrylate as the synergistic component. The copolymer is prepared by copolymerizing lauryl methacrylate and diethylaminoethyl methacrylate in concentrations 0 yield a product having 80% by weight of lauryl methacrylate and 20% by weight or diethylaminoethyl methacrylate. The polymerization is efiected by heating the reactants at about 140 F. for about ei hteen hours, with vigorous stirring in the presence of benzyl peroxide catalyst. The product is recovered as a straw colored, heavy viscous oil or" the general properties set forth in Table II.

Table II Viscosity at 210 F., SSU -2,200. Density, pounds/gallon 7.5. Color, N.P.A 1. Pour point, F to +10. Flash point (C.O.C.), F 380. Fire point (C.O.C.), F 420. Total acidity 0.0. Total base No., mg. KOH/g 8.0 (0.14 meq./g.). Ash, weight percent 0.00.

The polymeric condensation product prepared in the above manner and a mixture of phenothiazine were evaluated in other samples of the lubricating oil described in Example I. The evaluations were made in the same manner as described in Example I. The results are reported in the following table. For comparative purposes, samples 1 and 2 are repeated in this table.

Here again it will be noted that the polymeric condensation product (sample No. 5) by itself was of substantially no benefit. On the other hand, the mixture of the condensation product and phenothiazine (sample No. 6) served to increase the time to reach an acid number of 5 from 75 to 93 hours. Also, it will be noted that the percent viscosity change is lower for the synergistic mixture (sample No. 6) after 96 hours than for phenothiazine alone (sample No. 2) after 75 hours, as well as a reduction in the pentane insolubles down to zero for sample No. 6.

EXAMPLE HI The inhibitor composition of this example comprised phenothiazine as the antioxidant component and a polymeric condensation product of maleic anhydride with vinylmethyl ether, further reacted with decanol and finally reacted with Duomeen T as the synergistic component of the inhibitor composition. As hereinbefore set forth, Duomeen T is N-tallow-l,3-diaminopropane and predominates in alkyl groups containing sixteen to eighteen carbon atoms each. The copolyrnerization of maleic anhydride and vinylmethyl ether was effected in substantially the same manner as hereinbefore described. To 44 grams of the copolymer 80 grams of primary decanol were added and the mixture was heated, with stirring, to about 340 F. to effect esterification. 200 grams of xylene then were added and the resultant solution was refluxed for eight hours. 2.4 cc. of water were collected. 92 grams of Duomeen T then were added to the solution, after which refluxing and stirring were continued for six hours. A total of 8.5 cc. of water were collected. The solution then was filtered, distilled at a temperature up to 320 F. under 12 mm./Hg vacuum to remove xylene. The final polymeric condensation product containing a basic nitrogen was recovered as a heavy viscous dark oil, which is readily soluble in lubricating oil. The product contains 1.42 meg/g. of basic titratable nitrogen.

A synergistic mixture of phenothiazine and the polymeric condensation product prepared in the above manner were evaluated in another sample of the dioctyl sebacate in the same manner as described in Example I. The results are reported in the following table. For comparative purposes, samples 1 and 2 are repeated in thistable.

Here again it will be noted that the synergistic mixture (sample No. 7) increased the time required to reach an acid number of 5, as well as to considerably reduce the percent change in viscosity from 16.8 after hours for phenothiazine alone (sample No. 2) to 1.6% after 89.5 hours (sample N0. 7).

EXAMPLE IV As hereinbefore set forth, a synthetic lubricant being considered for use at high temperature is pentaerythritol ester. The pentaerythritol ester used in this example is available commercially from Hercules Powder Company as Hercofiex 600 and is stated to be monomeric pentaerythritol ester having an acid number of 0.10 maximum, a saponification number of 410, a refractive index at 20 C. of 1.453 and a specific gravity at 25/25" C. of 0.997.

The evaluations in the pentaerythritol ester were made in substantially the same manner as described in Example I for dioctyl sebacate. Sample No. 8 is a blank or control sample and did not contain any added inhibitor. Sample No. 9 contained 1% by weight of phenothiazine. Sample No. 10 contained 1% by weight of phenothiazine plus 1% by weight of the polymeric condensation product described in Example II. This synergistic mixture is the same as that used in sample No. 6 of TableIII. The results of these evaluations are reported in the following table:

Table V parative purposes, the blank or control sample (sample N0. 1) is repeated in the following table:

Hours Table VII Sample Additive to acid Percent viscosity No. number change 5 955 Hours Sample Additive to acid 8 None 16 g g 9 1% by weight of phenothiazine- 80 21.4after 77.5hours. 10 1% by weight oiphenothiazine 94 9.9 after 77.5 hours.

plus 1% by weight oftthe 10 None 9 p0 ymcrlc C011 EH58. 10D. I. product of Example IL 12 1755313315111: of 4,4 d1 scc butyldlaminodiphenyl 39 1's 1% by weight or 4,4-di-see-butyldiaminodiphenyl- 51 methane plus 1% by weight of the condensation roduct of Example 11. It will be noted that the synergistic mixture (sample 14 l lbyggeight of 4,4-dicyelohexyldiarninodlphen- 4s ymc one. 10) mcreas ed the hours acld number of 5 over 15 15 1% by weight of 4,4 dicyclohexyldiarninodiphen- 75 that obtained with phenothiazine alone (sample No. 9) ylrnctliiane plus 0.5%, byuf eght oflthlelpolyruer- 10 con ensa 10D pro no 0 xampe and also considerably reduced the percent change in V18 16 1% by weight of Mudicyclohexyldiammodiphfi 81 COSltY. nylmethane plus 1% by weight oi the polymeric V v condensation product of Example II.

EXAMPLE V 20 i A synergistic composition of phenothiazine and the icondensation product described in Example I was evaluated in the pentaerythritol ester described-in Example IV .7 The synergistic mixture is the same as sample No.

"4 of Table I. The results of this evaluation are shown in the following table. results of samples 8 and 9 are repeated in this table:

For comparative purposes the Table VI Hours Sample Additive to acid Percent viscosity No. number change None 16 1% by weight of phenothiazine. 80 21.4aiter 77 .5hours. 1% by weight of phenothiazine 149 15 after 99 hours.

plus 1% by weight of the condensation product of Example I.

Here again it will be noted that the synergistic mixture 7 (sample No. 11) considerably increased the time to reach an acid number of 5 to 149 hours as compared to 80 hours for 'phenothiazine alone (sample No'. 9), as well as reducing the percent change in viscosity to 15% after '99 hours as compared to 21.4% after 77.5 hours for phenothiazine alone.

EXAMPLE v1 7 As hereinbefore set forth, diaminodiphenylmethanes may be used as antioxidants in synthetic lubricants. Two diaminodiphenylmethanes were prepared 'as' follows: '4,4'- di-sec-butyl-diaminodiphenylmethane was prepared by the reductive alkylation of 4,4-diaminodiphenylmethane with crystallized from hexane and recovered as crystals having a melting point of 245 F., a basic nitrogen content of 5.50 mec /g. and a basic molecular weight of 363 (theoretical is 362). V w

The diaminodiphenylmethanes alone and synergistic mixtures of these with the polymeric condensation product prepared as described in Example H were evaluated in the dioctyl sebacate described in Example I. For com- From the data in the above table, it will be noted that the synergistic mixture served to increase the time to acid number of 5. In sample No. 15, 0.5% by weight of the synergist was used and this served to increase the time to acid number of 5 from 48 to 75 hours. Sample 16 reports the results when using 1% by weight of the synergist.

Although the diaminodiphenylmethanes are of lower potency when used alone than phenothiazine, it will be noted that the synergistic mixture in an amount of 0.5 by weight equaled the stability obtained with phenothiazine and with 1% by weight exceeded the stability obtained with phenothiazine. As hereinbefore set forth, in some applications this stability is adequate to meet the requirements and, in such cases, this synergistic mixture is used.

EXAMPLE VII The synergistic mixture of this example is 2,4'-di-secbutyl-diaminodiphenyl ether as the antioxidant component and the condensation product prepared as described in Example I as the synergistic component. These were evaluated in another sample of the dioctyl sebacate described in Example I. For comparative purposes, sample No. 1 is repeated in the table, which also reports the results of the diaminodiphenyl ether alone and when using the synergistic mixture.

Here again it will be noted that the synergistic mixture (sample No. 18) was considerably more effective than the antioxidant alone (sample No. 17) in extending the time in which the synthetic lubricant developed an acid number of 5.

EXAMPLE VIII The synergistic inhibitor of this example is a mixture of 4,4'-di-sec-butyl-diaminodiphenyl ether and the polymeric condensation product described in Example I. These were evaluated in another sample of the pentaerythritol ester and in the same manner as described in Example IV. For comparative purposes, sample No. 8 is repeated in the following table, which also reports the results of these evaluations.

Table 1X Hours Sample Additive to acid N 0. number 8 None 16 19 l%tlk 1y weight of 4,4-di-scc-butyldiaminodiphcnyl 45 e er. 20 1% by weight of 4,4-di-sec-butyldiaminodiphenyl 70 ether plus 1% by weight of the polymeric condensation product of Example I.

Again it is noted that the synergistic mixture considerably extended the time for the synthetic lubricant to develop an acid number of 5.

EXAMPLE TX 0.2% by weight of the synergistic inhibitor mixture described in Example I, and consisting of 50% by weight each of the antioxidant and synergist (sample No. 4) is incorporated in a lithium base synthetic grease. The grease is prepared by mixing 9% by Weight of lithium stearate with 90% by weight of dioctyl sebacate (Plexol 201). The mixture is heated at about 230 F., while agitating the same, and then is cooled to about 160 F., at which time 0.2% by weight of the synergistic inhibitor mixture is added. Agitation is continued and the mixture is allowed to cool to about 120 B, after which the grease is further cooled slowly to room temperature. The stability of the grease is tested according to a Norma-Holiman Method in which a sample of the grease is placed in a bomb and oxygen is charged thereto. The bomb then is heated to 212 F. and the time required for a drop of 5 pounds pressure is taken as the induction period. However, because the inhibitor of the present invention is very efiective in retarding deterioration, the run is stopped before a 5 pound drop in pressure is reached and the actual pressure drop at that time is reported.

When evaluated in the above manner, the lithium base synthetic grease containing the synergistic inhibitor composition will not develop a 5 pound drop in pressure for a considerably longer period of time than occurs in a sample of the grease not containing this inhibitor.

1 claim as my invention:

1. A synergistic oxidation inhibitor composition of one part by weight or" an antioxidant selected from the group consisting of phenothiazine, 2,4-di-sec-butyl-diaminodiphenyl ether and 4,4'-di-sec-butyl-diaminodiphenyl ether and from about 0.1 to about 4 parts by weight of the polymeric condensation product, formed at a temperature of from about 100 F. to about 175 F. of equimolar proportions of epichlorohydrin and N-alkyl amine having from about 14 to about 18 carbon atoms in said alkyl.

2. A synergistic oxidation inhibitor composition of one part by weight of phenothiazine and from about 0.1 to about 4 parts by weight of the polymeric condensation product, formed at a temperature of from about 100 F. to about 175 F, of equimolar proportions of epichlorohydrin and N-tallow amine.

3. A synergistic oxidation inhibitor composition of one part by weight of 2,4'-diasec-butyl-diaminodiphenyl ether and from about 0.1 to about 4 parts by weight of the polymeric condensation product, formed at a temperature of from about 100 F. to about 175 F., of equ-imolar proportions of epichlorohydrin and N-tallow amine.

4. A synergistic oxidation inhibitor composition of one part by weight of 4,4-di-sec-butyl-diaminodiphenyl ether and from about 0.1 to about 4 parts by weight of the polymeric condensation product, formed at a tempera- 14 ture of from about F. to about F., of equimolar proportions of epichlorohydrin and N-tallow amine.

5. A lubricating composition consisting essentially of a major proportion of a lubricant selected from the group consisting of dioctyl sebacate, pentaerythritol ester and lithium base grease and from about 0.001% to about 5% by weight of the synergistic oxidation inhibitor composition of claim 1.

6. A lubricating composition consisting essentially of a major proportion of dioctyl sebacate and from about 0.001% to about 5% by Weight of the synergistic oxidation inhibitor composition of claim 2.

7. A lubricating composition consisting essentially of a major proportion of dioctyl sebacate and from about 0.001% to about 5% by Weight of the synergistic oxidation inhibitor composition of claim 3.

8. A lubricating composition consisting essentially of a major proportion of dioctyl sebacate and from about 0.001% to about 5% by Weight of the synergistic oxidation inhibitor composition of claim 4.

9. A lubricating composition consisting essentially of a major proportion of pentaerythritol ester and from about 0.001% to about 5% by weight of the synergistic oxidation inhibitor composition of claim 2.

10. A lubricating composition consisting essentially of a major proportion of pentaerythritol ester and from about 0.001% to about 5% by Weight of the synergistic oxidation inhibitor composition of claim 3.

11. A lubricating composition consisting essentially of a major proportion of pentaerythritol ester and from about 0.001% to about 5% by weight of the synergistic oxidation inhibitor composition of claim 4.

12. A lubricating composition consisting essentially of a major proportion of lithium base grease and from about 0.001% to about 5% by weight of the synergistic oxidation inhibitor composition of claim 2.

13. A lubricating composition consisting essentially of a major proportion of lithium base grease and from about 0.001% to about 5% by weight of the synergistic oxidation inhibitor composition of claim 3.

14. A lubricating composition consisting essentially of a major proportion of lithium base grease and from about 0.001% to about 5% by Weight of the synergistic oxidation inhibitor composition of claim 4.

References Cited in the file of this patent UNITED STATES PATENTS 2,143,388 Schlack Jan. 10, 1939 2,198,961 Dietrich Apr. 30, 1940 2,214,352 Schoeller et al. Sept. 10, 1940 2,290,860 Burk et al. July 28, 1942 2,348,842 Paul May 16, 1944 2,454,547 Bock et a1 Nov. 23, 1948 2,695,222 Chenicek et al Nov. 23, 1954 2,698,316 Giammaria Dec. 28, 1954 2,737,496 Catlin Mar. 6, 1956 2,759,021 Gaar et ral Aug. 14, 1956 2,892,784 Harle et al June 30, 1959 2,892,786 Stewart et al June 30, 1959 3,017,258 Pollitzer I an. 16, 1962 FOREIGN PATENTS 545,072 Canada Aug. 20, 1957 OTHER REFERENCES Mode of Action of Phenothiazine Type Antioxidants, Murphy et al., I. & E. Chem., vol. 42, No. 12, December 1950, page 2479. 

1. A SYNERGISTIC OXIDATION INHIBTOR COMPOSITION OF ONE PART BY WEIGHT OF AN ANTIOXIDANT SELECTED FROM THE GROUP WITH AN AMOUNT OF A MEMBER OF THE GROUP CONSISTING OF PHENY ETHER AND 4,4''-DI-SEC-BUTYL-DIAMONIODIPHENYL ETHER AND FROM ABOUT 0.1 TO ABOUT 4 PARTS BY WEIGHT OF THE POLYMERIC CONDENSATION PRODUCT, FORMED AT A TEMPERATURE OF FROM ABOUT 100*F. TO ABOUT 175*F. OF EQUIMOLAR PROPORTIONS OF EPICHLOROHYDRIN AND N-ARYKLY AMINE HAVING FROM ABOUT 14 TO 18 CARBON ATOMS IN SAID ALKYL. 